We haven't seen it. Could it be IR interference? Or a sticky remote button?

Frankly, it does sound like the problem is in the unit since it works on reboot.

Have you tried switching the settings to use the remote via RF instead of IR?

I have experienced precisely the same problem with a one-week old HR21. The HR21 remains functional, but will not respond to the hand-held remote, or a slingbox pro IR remote (controlled from the computer), or the front buttons on the unit. Only the red "reset" button makes the unit respond to the remote again (which in my case requires a walk to a different floor of our house since the HR21 is located in our utility room). I am guessing there is a problem with the HR 21, but will send a separate email to Weaknees for suggestions. So far, this has happened about once per day or every other day.

As in the email - we'd recommend moving the Slingbox IR dongle away completely and seeing if the problem happens again.

Remote Failure -- Update

After my prior post on the spontaneous failure several times of my new HR21 to respond to the remote control, the problem has only recurred once more over a period of approximately four weeks (and the recurrence involved an overall "freeze" of the HR21) and the HR21 has otherwise been stable and reliable.

The only ongoing problem is that, unlike two TIVO DirecTV DVR units -- which invariably start recording at precisely the start time of any problem -- my HR21 (and a separate HR20) both have a "start time" problem involving the commencement of recording times approximately 10-15 seconds late, after the start of the program in question. Although one work-around can be setting the start time (when recording) to one minute early, this creates a separate problem of causing unnecessary recording conflicts. From my review of other web sites, this "start time" issue appears to be a known problem with the HR20 and HR21 that has no known current fix, but I would be grateful for any suggestions.